Polyurethane foams are widely known and used in automotive, housing and other industries. Such foams are produced by reaction of a polyisocyanate with a polyol in the presence of various additives. One such additive is a chlorofluorocarbon (CFC) blowing agent which vaporizes as a result of the reaction exotherm, causing the polymerizing mass to form a foam. The discovery that CFC's deplete ozone in the stratosphere has resulted in mandates diminishing CFC use. Production of water-blown foams, in which blowing is performed with CO.sub.2 generated by the reaction of water with the polyisocyanate, has therefore become increasingly important. Tertiary amine catalysts are typically used to accelerate blowing (reaction of water with isocyanate to generate CO.sub.2) and gelling (reaction of polyol with isocyanate).
The ability of the tertiary amine catalyst to selectively promote either blowing or gelling is an important consideration in selecting a catalyst for the production of a particular polyurethane foam. If a catalyst promotes the blowing reaction to a too high degree, much of the CO.sub.2 will be evolved before sufficient reaction of isocyanate with polyol has occurred, and the CO.sub.2 will bubble out of the formulation, resulting in collapse of the foam. A foam of poor quality will be produced. In contrast, if a catalyst too strongly promotes the gelling reaction, a substantial portion of the CO.sub.2 will be evolved after a significant degree of polymerization has occurred. Again, a poor quality foam, this time characterized by high density, broken or poorly defined cells, or other undesirable features, will be produced.
Tertiary amine catalysts generally are malodorous and offensive and many have high volatility due to low molecular weight. Release of tertiary amines during foam processing may present significant safety and toxicity problems, and release of residual amines from consumer products is generally undesirable.
Amine catalysts which contain primary and/or secondary hydroxyl functionality typically have limited volatility and low odor when compared to related structures which lack this functionality. Furthermore, catalysts which contain hydroxyl functionality chemically bond into the urethane during the reaction and are not released from the finished product. Catalyst structures which embody this concept are typically of low to moderate activity and promote both the blowing (water-isocyanate) and the gelling (polyol-isocyanate) reactions to varying extents. Examples of such structures are included in the following references: U.S. Pat. Nos. 4,957,944; 5,071,809 and 5,091,583.
Secondary alcohols are preferred in the structures, because these catalysts exhibit a desirable balance between their promotion of the active hydrogen-isocyanate reactions and their own reactivity with isocyanates. In contrast, catalysts which contain primary alcohols react rapidly with isocyanates and thus high use levels are required. Catalysts which contain tertiary hydroxyls react slowly with isocyanates, but the urethanes of tertiary hydroxyls which are formed have poor thermal stability. These urethanes may degrade and release the catalyst at temperatures substantially below the decomposition temperature of the foam itself. The free amine could then accelerate foam decomposition.
A catalyst which strongly promotes the water-isocyanate (blowing) reaction is advantageous for the manufacture of many polyurethane foams. Such catalysts include the .beta.-(N,N-dimethylamino)alkyl ethers, in particular bis(dimethylamino)ethyl ether. Low odor, reactive catalysts structurally related to bis(dimethylamino)ethyl ether are described in U.S. Pat. Nos. 4,338,408 and 4,433,170. In particular, 2-[N-(dimethylaminoethoxyethyl)-N-methylamino]ethanol, Texacat.RTM. ZF-10 catalyst, is an effective blowing catalyst, albeit less effective than bis(dimethylamino)ethyl ether.
Linear, permethylated di-, tri-, and polyamines are also known to promote the water-isocyanate reaction.
U.S. Pat. No. 3,836,488 discloses the use of tris[2-(dimethylamino)ethyl]amine as a catalyst for making urethanes by reacting polyisocyanate with active hydrogen containing compounds.
U.S. Pat. No. 4,143,003 discloses a process for the production of polyurethane foam resins in which linear polyamines containing at least 4 tertiary nitrogen atoms are used as catalysts. Such catalysts include hexamethyltriethylenetetramine and heptamethyltetraethylenepentamine.
U.S. Pat. No. 5,039,713 discloses a blowing catalyst consisting essentially of 25 to 80 wt % pentamethyldiethylenetriamine and 20 to 75 wt % bis(dimethylaminopropyl)methylamine.
U.S. Pat. No. 4,026,840 discloses that the reaction of isocyanate with polyols to form polyurethanes and their polymerization to polyisocyanurates are promoted by certain hydroxyalkyl tertiary amine catalysts corresponding to the formula: ##STR2## wherein Y is CH.sub.3 or Z,
Z is --CH.sub.2 CH.sub.2 OH, and PA1 n is 1 or 2. PA1 n is an integer from 0 to 3. PA1 n is an integer from 1 to 8.
EP 0 469 545 A2 (U.S. Pat. No. 5,229,430) discloses an amine catalyst for producing polyurethane comprising a compound of the general formula: ##STR3## wherein R.sub.1, R.sub.2 and R.sub.3 respectively and independently are alkyl groups having 1 to 3 carbon atoms, and
The amine catalyst has a secondary hydroxyl group in the molecule and is claimed to be non-bleeding in the polyurethane resin.
Alkylene oxide adducts of polyamines are also used as polyols for the production of polyurethanes.
U.S. Pat. No. 5,064,957 discloses the hexakis propylene oxide adduct of tris(2-aminoethyl)amine as a precursor to the morpholine-containing polyurethane catalyst, but the propylene oxide adduct itself is not noted as having catalytic activity.
N. Malwitz, et al, J. Cell. Plastics, 1987, vol 23, pp 461-502, compared Me.sub.2 NCH.sub.2 CH.sub.2 N(Me)CH.sub.2 CH.sub.2 OH and Me.sub.2 NCH.sub.2 CH.sub.2 N(Me)CH.sub.2 CH.sub.2 CH.sub.2 OH and found that the hydroxypropyl group shifted the selectivity toward gelling.